The handful of times I've attended a spin class I just used the platform side of the pedals with the straps. Cinched them up tight and they worked fine. It's not like I needed to unclip in a hurry at stoplights or an emergency.

Which brings back the memory of my very first spin class. I showed up all cocky thinking it would be a walk in the park. I stumbled out of the room an hour later with my butt completely kicked. The worst part was, the lady leading the class who did the entire workout along with the rest of us was hardly sweating - and looked to be about eight months pregnant.